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Wednesday, 10 November 2021

Surprise: the Big Bang isn’t the beginning of the universe anymore


In the beginning, there was … well, maybe there was no beginning. Perhaps our universe has always existed — and a new theory of quantum gravity reveals how that could work.

"Reality has so many things that most people would associate with sci-fi or even fantasy," said Bruno Bento, a physicist who studies the nature of time at the University of Liverpool in the U.K.

In his work, he employed a new theory of quantum gravity, called causal set theory, in which space and time are broken down into discrete chunks of space-time. At some level, there's a fundamental unit of space-time, according to this theory. 

Bento and his collaborators used this causal-set approach to explore the beginning of the universe. They found that it's possible that the universe had no beginning — that it has always existed into the infinite past and only recently evolved into what we call the Big Bang.

A quantum of gravity

Quantum gravity is perhaps the most frustrating problem facing modern physics. We have two extraordinarily effective theories of the universe: quantum physics and general relativity. Quantum physics has produced a successful description of three of the four fundamental forces of nature (electromagnetism, the weak force and the strong force) down to microscopic scales. General relativity, on the other hand, is the most powerful and complete description of gravity ever devised.

But for all its strengths, general relativity is incomplete. In at least two specific places in the universe, the math of general relativity simply breaks down, failing to produce reliable results: in the centers of black holes and at the beginning of the universe. These regions are called "singularities," which are spots in space-time where our current laws of physics crumble, and they are mathematical warning signs that the theory of general relativity is tripping over itself. Within both of these singularities, gravity becomes incredibly strong at very tiny length scales.

As such, to solve the mysteries of the singularities, physicists need a microscopic description of strong gravity, also called a quantum theory of gravity. There are lots of contenders out there, including string theory and loop quantum gravity.

And there's another approach that completely rewrites our understanding of space and time.

Causal set theory

In all current theories of physics, space and time are continuous. They form a smooth fabric that underlies all of reality. In such a continuous space-time, two points can be as close to each other in space as possible, and two events can occur as close in time to each other as possible.

    "Reality has so many things that most people would associate with sci-fi or even fantasy."
    Bruno Bento

But another approach, called causal set theory, reimagines space-time as a series of discrete chunks, or space-time "atoms." This theory would place strict limits on how close events can be in space and time, since they can't be any closer than the size of the "atom."

For instance, if you're looking at your screen reading this, everything seems smooth and continuous. But if you were to look at the same screen through a magnifying glass, you might see the pixels that divide up the space, and you'd find that it's impossible to bring two images on your screen closer than a single pixel.

This theory of physics excited Bento. "I was thrilled to find this theory, which not only tries to go as fundamental as possible — being an approach to quantum gravity and actually rethinking the notion of space-time itself — but which also gives a central role to time and what it physically means for time to pass, how physical your past really is and whether the future exists already or not," Bento told Live Science.

Beginning of time


Causal set theory has important implications for the nature of time. 

"A huge part of the causal set philosophy is that the passage of time is something physical, that it should not be attributed to some emergent sort of illusion or to something that happens inside our brains that makes us think time passes; this passing is, in itself, a manifestation of the physical theory," Bento said. "So, in causal set theory, a causal set will grow one 'atom' at a time and get bigger and bigger."

The causal set approach neatly removes the problem of the Big Bang singularity because, in the theory, singularities can't exist. It's impossible for matter to compress down to infinitely tiny points — they can get no smaller than the size of a space-time atom. 

So without a Big Bang singularity, what does the beginning of our universe look like? That's where Bento and his collaborator, Stav Zalel, a graduate student at Imperial College London, picked up the thread, exploring what causal set theory has to say about the initial moments of the universe. Their work appears in a paper published Sept. 24 to the preprint database arXiv. (The paper has yet to be published in a peer-reviewed scientific journal.) 

The paper examined "whether a beginning must exist in the causal set approach," Bento said. "In the original causal set formulation and dynamics, classically speaking, a causal set grows from nothing into the universe we see today. In our work instead, there would be no Big Bang as a beginning, as the causal set would be infinite to the past, and so there's always something before."

Their work implies that the universe may have had no beginning — that it has simply always existed. What we perceive as the Big Bang may have been just a particular moment in the evolution of this always-existing causal set, not a true beginning.

There's still a lot of work to be done, however. It's not clear yet if this no-beginning causal approach can allow for physical theories that we can work with to describe the complex evolution of the universe during the Big Bang.

"One can still ask whether this [causal set approach] can be interpreted in a 'reasonable' way, or what such dynamics physically means in a broader sense, but we showed that a framework is indeed possible," Bento said. "So at least mathematically, this can be done."

In other words, it's … a beginning.

Reference:

If time had no beginning by Bruno Valeixo Bento, Stav Zalel arxiv.org/abs/2109.11953

3 comments:

  1. I explained a very similar theory on my blog back in 2020, light as a chain reaction through a quantized space manifold.

    Only I think my description was much more compelling and complete, considering a couple articles with diagrams and images that work together to paint the big picture.

    https://stephenkronstein.wordpress.com/2020/08/28/light-as-a-chain-reaction/

    I wrote:

    I now understand the fabric of space to be envisioned at the quantum level where modality is linked together as a Flower of Life.

    A photon is really a chain reaction through the fabric rather than an individual particle travelling a distance, like Newton’s cradle where only the kinetic energy transfers from the first knocking ball through to the last, not the ball itself.

    These days people understand that the strings in string theory are usually described as bands or loops of vibrating energy. I’m thinking that these bands form a daisy chain of looping energy connecting one quantum [quantized] space to the next in the cosmic Flower of Life...

    ...photons are not actually particles but rather vibrating/looping bands of energy — aka “strings” — appearing as these modality intersections, what are opportunities for a chain reaction to occur through the contraction-expansion oscillation of the energy passing through the string.


    And more specifically, to imaging how this might look in terms of the Big Bang etc, I published this other article, Universe envisioned:
    https://stephenkronstein.wordpress.com/2020/08/23/universe-envisioned/

    I wrote:

    ...I see what’s going on, how the physical limits of the universe can be envisioned...

    Now we can relate this to the electromagnetic field, this second image (see link), basically describing the same event of how the universe takes its physical form, or so I understand.

    That area called the Equator Plane, indicated by the cloudy disk at centre, this is where I suspect the Higgs boson does it’s thing, adds the mass that slows down the otherwise massless particles creating the ring of reality — the now — and I guess a holodeck of zeros and ones.

    The Equator Plane is what I understand bisects the area where the two fields are in contact. The whole of this is basically a representation of the shape of the manifold whereon the math of the universe unfolds. (see image in article)

    ...perhaps with something of a blackhole/wormhole at its centre...

    The darkness at its outer edge is expanding faster than the speed of light as it leaves the Equator Plane. This is the edge of the physical Universe where those particles lose pressure strength and fling off into the manifold as massless only to recycle back into the vortex of the torus on the other side, and eventually back towards the centre of the Equator Plane, where the particle once again is affected/slowed by the Higgs boson, aka God particle, by gaining mass to perform as reality.


    sk

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  2. Causal set theory is a very strong contender among a multitude of theories about the beginning of tspacetime.Lee Smolin has written insightful about this theory

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  3. In the blackbody radiation problem at the turn of the previous century, the "ultraviolet catastrophe" as it was called was a problem like today's singularities in a black hole and at the beginning of the creation of our Universe. The problem back then was solved in a novel way by Max Planck by proposing that ENERGY like perhaps SPACETIME of today in casual set theory comes in discrete chunks or quanta given by the formula E = hf. My question is this. Can we use Planck's approach or equation to write something similar like perhaps instead of Energy = constant x frequency we can write (spacetime length metric) = constant x (energy)?
    That way, spacetime depends directly on the amount of mass-energy as per the Theory of General Relativity demands.

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